The present invention relates to the inspection of glass bottles to identify flaws in the bottom of the bottles. A diffused light source directs light upwardly through the bottom of the bottle and a two dimensional camera looks at the illuminated bottom through the bottle mouth to see any defect.
A glass bottle may have a wide disparity of thicknesses in the base. A glass bottle may, for example, have a heavy heel portion. As a result, the camera will see varying light intensities and may not see enough light in the heel region to see the defects. To see these defects, the intensity of the light must be increased but the intensity level of the light passing through the thin portions may present a dynamic brightness range (contrast ratio) beyond the capabilities of the camera. This dynamic brightness range can be reduced by matching the spectral composition of the light to the spectral absorption of the bottle glass by passing the light through a colored filter matching the color of the bottle.
When spectral matching of the light source to the bottle does not sufficiently reduce the contrast ratio to fall within the dynamic brightness range of the camera, spot or ring filters designed for the application may be applied to overlay the light source to attenuate the light from the backlight source in a pattern which corresponds to those areas of the bottle which are transmitting too much light and overloading the sensor in the corresponding image regions.